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Old 08-01-2020, 12:32 PM   #1
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2018 27' Globetrotter
Mooresville , North Carolina
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Which Battery is better - or neither?

My boat has 2 batteries. I alternate use based on even and odd days. If an odd day I use battery #1, even I use battery #2. Battery 2 is starting to slow down in it's cranking ability but otherwise still functions. I use a trickle charger to keep both batteries charged over the winter and this has extended my battery lives from 3 yrs to 8 yrs. Battery #2 is an 8 yr old Group 24 Interstate battery and has a 12.4V reading when it is at rest. My battery #1 returns 12.8V at rest so it is good.

My Airstream has the factory solar and included 2 Lifeline Group 24 AGM batteries. They are 2 years old. Recently, I tested the voltage at rest for each. 1 battery had 12.9V at rest and the other 12.2V. I had thought the batteries were doing OK but I thought AGM's should be doing better than what they had been. Turns out the bad battery was the issue. Lifeline sent me a prorated replacement battery that matches the 12.9V at rest of my other battery. The AGM batteries have 800 cranking amps, as does my Interstate non-AGM battery.

I had been planning on replacing my boat battery #2 at some point. I was wondering if the old AGM could be used as a replacement battery for it? I was expecting the AGM to return a higher voltage that the Interstate but it did not. I have heard that AGM's are better long term than non-AGMs. I realize the age of my Interstate is at/near the end.

My question - Is a 2 year old AGM battery that returns 12.2V at rest better than a 8 yr old non-AGM battery that returns 12.4V at rest? Or, are both of these batteries ones that should be scrapped?
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Old 08-01-2020, 03:33 PM   #2
2016 19ft flying cloud
 
Spokane , Washington
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If the two boat batteries are over eight years old, I’d replace both,,,Costco has them on sale for under $100 each
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Old 08-01-2020, 03:36 PM   #3
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How long are you waiting to check voltage after disconnectIng power? Should wait a couple hrs to get a true reading
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Old 08-01-2020, 03:51 PM   #4
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Quote:
Originally Posted by Spinonedad View Post
How long are you waiting to check voltage after disconnectIng power? Should wait a couple hrs to get a true reading
I waited a full day. The AGM will get up to 12.7 after a charge but always settles back to 12.2V. I just thought AGMís have more cycles than regular lead acid batteries so it should hold its 12.2 longer than the interstate can hold its 12.4. However; I donít think the 12.2V will deliver what I need.

Just thought Iíd throw it out there for persons more knowledgeable than I.
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Old 08-02-2020, 09:40 AM   #5
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Hi

The right way to manage the batteries in the AS is to keep them in parallel all the time. You never use them / charge them one at a time in an AS.

If you replace one battery in a pair, you really should also replace the other one. Batteries with different wear histories will not balance well. The result is that one will do most of the work and wear out quickly ....

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Old 08-02-2020, 11:03 AM   #6
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You need a computer charger with 2-4-8 volt charge selections, battery type selection, and desulfator. I have one made by Battery Minder. It will bring old AGMs back in just a few days. My boat's cranking battery (an Optima 24) was getting weak, but the desulfator saved it. AGMs really ought to read 13.2v resting, if in good health. Also, GM has recommended only replacing one parallel battery at a time as long as the the other(s) test OK. I have been doing that for 8 or 10 years now will good results. Its much cheeper too.
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Old 08-02-2020, 02:43 PM   #7
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2020 30í Globetrotter
Phoenix , Arizona
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Iíve been stressing over my batteries and maintaining the right charge. My 2020 GT 30í is 130 miles away at a RV park in the forest. I have neighbors checking a voltage meter i installed. Iíve learned voltage is not accurate. Right after i bought it the convertor went out and ruined our food. We go up every two weeks.

So after much research Iíve come up with the following solution.

I have a hotspot always on (1/4 mile from cell tower). I added a rvwhisper box connected to hotspot. I built the attached gizmo. 3 PowerMon Bluetooth units. One for total RV amp/watt draw. One for Solar only, last one inverter. I intend to Velcro to the underside of battery box. Cables may need to be shorter but Iíll deal with that when i get there. I used 4, 6, 10, 12 and 16 gauge wire based on max amp draw. I have a 60 amp fuse in the house battery. Both inverter and solar are protected in the trailer. All connections are appropriate size crimped and heat shrink. Iíve tested the connection at home with my car. Signal going thru hood, 2 walls and window i can be 25 feet away. I intent to put the rvwhisper under the front sofa. 4 feet from PowerMon devices.

Wish me luck!

I can monitor it all from a phone app hundreds of miles away. It will also send me a text when the fridge gets too hot or shore power quits. Once i analyze the data i will know for sure how long the solar will keep it up. Since i have a 12v fridge Iím hoping 20-24 hours. Lots of sun up there. Plenty of time to get up and run generator. Iíll keep you posted.

Jim
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Old 08-02-2020, 03:11 PM   #8
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LiON is the future for all batteries
the next set will be soild state Li models in 2-5 years
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Old 08-02-2020, 04:10 PM   #9
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If possible, can afford, when your boat batteries go bad, replace them with the trailer batteries. Since you have two, you can use them until they are really shot. Put a 100ah lithium in your trailer. Approximately doubles your useable ah.
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Old 08-02-2020, 04:49 PM   #10
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12.2 indicates onset of a bad cell, 12.4 could be excessive sulfacation. I'd put it on a charger that can maintain 14.6-14.8 V for 12 hours and check it again. You may be able to get some more life out of it.

The trickle charger doesn't deliver enough current to prevent or reverse acid stratification and sulfacation.
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Old 08-04-2020, 06:26 AM   #11
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12.2 indicates onset of a bad cell, 12.4 could be excessive sulfacation. I'd put it on a charger that can maintain 14.6-14.8 V for 12 hours and check it again. You may be able to get some more life out of it.

The trickle charger doesn't deliver enough current to prevent or reverse acid stratification and sulfacation.
Thanks Brian!
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